Fluorescent lamp circuit



April 22, 1952 l.. G. LEGORRETA ET AL 2,593,576

FLUOFESCENT LAMP CIRCUIT Filed May 28, 1949 atentec pr. l22, 1952 UNITEDSTATES PATENT oFF-ICE FLUoREscEN'r LAMP CIRCUIT Luis G. Legorreta,Eduardo Pos'ada,`and Fernando Camarena, Mexico, City, Mexico, assignorsto Electrol S. A., Mexico corporation City, Mexicoea Mexican ApplicationMay 28, 1949, -Serial No. 96,028

l In Mexico October 16, 1948 3 claims. (01. 315-266) f flow isinitiated, this heating of the lamp lai ment may be discontinued.Whether this external source heating 'is discontinued or not, a secondproblem `then arises, inthat due to the reversal of the currentoccurring atV each halfcycle of the A. C. potential during operation,the use of individual lamps connected conventionally tothe potentialsupply results in a stroboscopic illumination effect which is tiring tothe human eye and causeseyestrain. The prior art solved this secondproblem partially by operating a plurality of lamps spaced closelyadjacent one another and by arranging the circuit connections tothe endsockets of these lamps so that opposite ends of alternate lamps werephased similarly. This resulted in roughly the same amount ofillumination at all times adjacent either end of any two adjacent lamps,and

the resultant illumination from the plurality of lamps couldvbe furthersmoothedj by :introducing a ground glassin the path ofthe illumination.Y y

Briefly, our invention provides a fluorescent lamp circuit which botheliminates the initial heating. of the fluorescent lamp iilamentgandproducesgillumination without stroboscopic effect from an,v individualfluorescent lamp by causing the current to ow uni-directionally of thelamp from the filament or Vcathode alternately to two anodes provided atthe other end of the lamp. The current passing through the tube also4passes alternately through two inductance windings wound on a commoncore, which limit the value of the currentv and smooth out the rectifiedcurrent fluctuations. In addition these induc'tance windings may beutilized at startingto produce, bytransformer action, Van additionalinstantaneous voltage, which when added to the applied A. C. voltage isgreater than the breakdown voltage of the lamp and causes it to begin tooperate as a light source.v

Our invention will be more apparent from the following ,description whentaken in connection? with the accompanying drawings, inwhich Fig.1-shows one embodiment of this invention with, the fluorescent lampvconnected properly;4

Fig. 2 shows the circuit of Fig l with a fluorescent n'lamp connected inthe improper orinverted position;

Fig. 3 shows a second embodiment of this ing vention. which differs fromthe embodiment -of Fig l in the substitution of a condenser forinitiating the starting of the lamp operation; l Fig. 4 shows a thirdembodiment with a nuorescent lamp insertedl inthe circuit inone oper-V4ative position; V Y

Fig. 5 shows the embodiment of Fig. 4 with thel fluorescent lampinserted in the other or inverted operative position.

In Fig. 1v is lshown a fluorescent lamp I0 connected in., circuit withan auto-transformer II and a combined relay-inductance I2. Fluorescentlamp II) has a filament-type cathode I5 at one end and two adjacentanodes I6`and I1 at the other end thereof. Combined relay-inductanceI2.` has two similar windings, phased as indicated by the d ots adjacentone end of each as Vshown in the drawing, and both wound-on acommoncore. vA relay armature I8 is biased normally, as by means of spring I9,to engage Xed contact 2G in the absence of a current flow through thewindings ofthe inductance. When a current does flow through either orboth windings of combined relay-inductancehlZ, the magnetic iiux therebyproduced attracts the armature I8 and disengages its contact from fixedcontact 20. One end of the winding o f -auto transformer I I isconnected through one winding` of inductance I2 to anode IE, and theother end ofthe windingl of auto-transformer Il -is con-, nected throughthe other winding of inductance I 2 to anode I'I and through armature' I8 and xed contact 2] to anode I6. The tap of auto-transformer` I isconnected to one terminal of lament I5, and the A.YC. potentialsupply'is connected tothe other terminal of filament I5 and thatend ofthe winding of auto-'transformerf'i I.. which is connected to armatureI8. .Preferably both windings of combined relay-inductan'ce yI',2haveothesarne number of turns or, in other words,` a turns ratio of 1:1,and the tap of auto-trans-` former II is preferably positioned at thevcenter of its winding or, in other words, is a center-tap. Theimpedance of filament I5 is small with respect to the impedance of thatportionfofthe winding of auto-transformer II across vI/hich the A.` C.potentiall is applied, and hence there -is no appreciable voltage dropacross filament I5. Thus,'filament I5 is notheated initially for.start-i' ing or caused to glow, and operates as a cold cathode ratherthan a thermionic one. The generally accepted theory is believed to bethat when the extra starting voltage is applied between the cathode andthe anodes, a hot point of emission is produced at some point on thecathode, which causes the latter to emit electrons and the lamp hence tobegin to emit visible light.

Initially, before the A. C. potential is applied to this circuit, aswell as at the instant when the potential is applied, armature I8 andxed contact 20 are engaged due to the biasing action of spring I9. Atthe instant of applying .the A. C. potential, a voltage equal to twicethe supply voltage is produced across the auto-transformer winding, andthis voltage is applied to the righthand coil of inductance I2momentarily dueto the completion of the circuit through armature I8 andfixed contact 2E). This voltage applied across the right-hand winding ofinductance I2 induces an equal and correspondingly-phased voltage in theleft-hand coil of inductance I2. During the half cycle when theleft-hand end of auto-transformer II is positive with respect to itscenter-tap, the resultant voltage induced in the left-hand coil ofinductance I2 is of such polarity that it adds to, rather than subtractsfrom, the voltage produced between the autotransformer tap and theleft-hand end of its coil or winding. Thus, at this moment, there isapplied between the filament or cathode I and the anode I'I a voltageequal to approximately three times the supply potentia1 and this, beinggreater than the breakdown potential of the gas in the fluorescent lampI0, causes the lamp to light. The ow of current through the inductanceI2 at the same time causes armature I8 to disengage from contact 2IJ,and the fluorescent lamp III then continues to operate with auni-directional current flow along its length from filament I5 to anodesI6 and II alternatively, depending upon which end of auto-transformer II is positive with respect to the tap thereof at any instant. Shouldfluorescent lamp I0 fail to pass current or start before armature IBdisengages from xed contact due to the momentary current fiowing in theright-hand coil of inductance I2 because of the voltage applied acrossit from the entire winding ofV auto-transformer II, armature I8 willimmediately again engage xed contact 20 and continue this alternatedisengagement and engagement until the lamp passes current, whereuponarmature I8 will remain disengaged from fixed contact 2G, as explainedabove. Ordinarily, fluorescent lamp I0 will start to operate as soon asan A. C. potential is applied to the circuit as shown, but at times,particularly when the fluorescent lamp I0 is cold, armature I8 maydisengage and engage xed contact 20 several times before the lamp startsto operate.

Fig. 2 shows the same circuit as Fig. l but with the fluorescent lamp Itinverted in its end sockets (not shown) so that the lamp is connected inthe circuit as shown. This illustrates an important feature of ourcir-cuit of this embodiment, since inversion of the lamp in its socketscannot cause damage to the circuit or to the lamp inasmuch as `there isthen no connection to the auto-transformer II from the A. C. supplybecause of the open circuit between anodes IS and I1. If the lamp I0 isinadvertently inserted in its sockets (notv shown) in this position, allthat is necessary to start theoperation of the lamp is to reverse. it-

end-for-end in the sockets, whereupon it will be in operative position,as in Fig. 1.

In Fig. 3 is shown another embodiment of our invention similar to theembodiment of Fig. 1 but with a condenser 2i utilized for startingpurposes and the -combined relay-inductance I2 of the embodiment of Fig.1 replaced by an inductance I2', which again has two similar windingswound on a common core and phased as before, as indicated by the dotsadjacent corresponding ends of the inductance windings. Condenser 2I isconnected between anode I6 and the tap on auto-transformer i I. Theremaining connections are the same as in the embodiment of Fig. 1, aswill be apparent from an inspection of the drawing.

The explanation of the operation of this embodiment is believed to be`as. follows. When the A. C. potential is applied to this circuit,during the half cycle that the right-hand A. C. supply line is positivethe tap of the auto-transformer II is also positive, and this charges upthe condenser 2i so that its upper plate and the upper end of theright-hand coil of inductance I2 are positive. During the next halfcycle, the left-hand A. C. supply line is positive with respect to theautotransformer tap. At the same time a voltage is induced in theleft-hand coil of inductance I2. due to the charge remaining uponcondenser 2 I, which adds to the voltage applied between the left-handend of auto-transformer I I and the tap thereof so that at this instanta voltage appreciably greater than the supply voltage is applied betweenthe filament I5 and yanode II. This voltage, being greater than thebreakdown voltage of the lamp, again starts a uni-directional currentflow through the tube. Thereafter, the tube operates as above with thecurrent owing uni-direction-ally along the length of the tube betweenfilament I5 and anode I6 or I'I, depending upon which end ofauto-transformer II is positive at any instant.

In Fig. 4 is shown another embodiment of our invention similar to theembodiment of Fig. l but with auto-transformer I I replaced by atransformer Il having separate primary and secondary windings with theircorresponding ends polarized as indicated by the dots in the drawing.Preferably the primary and secondary of transformer II have a turnsratio of 1:1. Combined relay-inductance I2" is similar to combinedrelay-inductance I2 of Fig. l except that one of its windings or coilsis tapped, preferably at the center thereof. One end of the primarywinding of transformer I I' is connected to one line of the A. C.supply, to anode I'I and to xed contact 2. The oppositely-phased end ofthe secondary winding of transformer I I is connected to anode I6, andthe other end of this secondary winding is connected to one end of thetapped coil of combined relay-inductance I2. The correspondingly-phasedend of the other coil of inductance I2" is connected to the other A. C.supply line and to the free end of the primary winding of transformerII'. The other end of the tapped coil is connected to one terminal offllament I5, and the tap thereof is connected to armature I8. The otherterminal of filament I5 is connected to the free end of the otherwinding or coil of inductance I2.

Before the A. C. potential is applied to this circuit, as well as at theinstant when the potential is applied,V armature I3 engages xed contact20 dueto the biasing action of spring I9. Durwinding, said transformersecondary winding, said iamentary cathode, and said engaged con-.-tacts, said engaged contacts thereupon disengage due to the currentpassing through the windings of said relay inductance, and saiduorescent lamp thereafter remains lighted without stroboscopic effect.due to the full-wave rectication of the current flowing through said`lamp.

3. A circuit for operation of gas-lled fluoresf cent lamps comprisingthe combination of .a transformer having a primary and a secondarywinding, a combined relay-inductance having a first tapped winding asecond winding wound'gn a common core and including a-n armature andcontacts separated by magnetic attraction be,- tween the core andarmature when current ,ows in said .relay .inductanoe windings but thearmature beine biased to brine the .contacts ,into .erieaeement normallyinthe ,absence of Current flow in `saiol relay inductance windings, theeolitaois when in engagement connecting the tap of l seid first rela-yindueiance winding with one end of said transformer primary winding, aconnection between the similarly-phased end of said transformerSecondary winding ,and one epd of seid first tapped relay indue'iarleewinding, and e corrnection between the correspondingly-phased end ofsaid Second Winding and the other end of Seid transformer primarywinding, whereby when en Af C, potentiel is applied to Seid transformerprimary -winding and .a ooresoent lamp. having. a lamentary cathode atone end and first and Second adjacent .enodes et the other end thereof,is connected With the filamentary cathode between the free enls of saidrelay inductaneewindings land its anodes to the free end of saidtransformer secondary Winding and the oppositel-yphased end o f saidtransformer primary Winding,

respectively, or with, its anodes to the freek endsv of said relayinductance windings, respectively, and its lamentary cathode betweentheV free end of said transformer secondary winding and theoppositely-phased end of said transformer primar ry winding, saidiuorescent lamp iscaused to light due to the transformer action of saidrelay inductance, said engaged contacts thereupon disengage due to thecuri-ent passing through the windings, of said relayY indue'anoe. and.Seid ,fluof rescent lamp thereafter remains lighted withoutstroboscopic effect due to the full-.wave rectification of the currentflowing through said lamp.

L. G. LEooaRE'rA.

Ef POSADA.

E CAMABENA- REFERENCES C11-11D The following references are of record inthe file of this patent:

UNTTED sTATEs PATENTS Number Name Date 949,335 Thomas Feb. 15, 19101,905,840 Forney Apr. 25, 1933 1,930,083 Buttolph Oct. 10, 19331,930,086 Forney. oct. 10, 1933 1,960,349 schabene May 29, 19341,961,754 Forney June 5, 1934 1,977,254 Swart Oct. 16, 1934 1,984,483Kenty Dec. 1s, 1934 2,170,446 Edwards Aug. 22, 1939 2,170,456 Lord Aug.22, 1939 2,177,383 Foulke oct; 31, 1939 2,429,162 Keiser Oct. 14, 19472,439,976 Keiser Apr. 20, 1948 2,444,408 Larime June 29, 1948

